On some properties of the proportional fair scheduling policy

The proportional fair (PF) scheduling algorithm has been proposed as a technique to improve the throughput of multiple packet-data users sharing a wireless downlink channel while preserving fairness. It exploits the fact that the propagation channels between the base station (BS) and the mobile stations (MS) fade independently giving rise to "multi-user diversity". The gain offered is significant when the allowed packet delay exceeds the de-correlation time of the fading channels and the number of users is high. In this paper we investigate analytically the "time allocation" property and the multi-user diversity gain of the PF algorithm under certain conditions in the context of the HSDPA standard. Since in practical systems a certain latency is unavoidable, we have studied the use of a "backoff" factor to reduce the probability that when the transmission takes place, the channel will not be able to support it.